Because female birds can lay eggs regardless of whether they are fertilized, however, each partner in a lesbian pair usually contributes a full clutch of eggs to their nest even if she hasn't mated with a male. As a result, female homosexual pairs often lay what are called supernormal clutches, that is, double the number of eggs usually found in nests of heterosexual pairs.¹⁰
10. Supernormal clutches have also been reported for pairs of male Emus, probably because more than one female has laid in their nest. What might be termed "subnormal" clutches – i.e., nests containing fewer eggs than are usually found for heterosexual pairs – are reported for female pairs of Blue Tits. And "super-supernormal" clutches occasionally occur in heterosexual pairs of Roseate Terns: as a result of within-species parasitism and possibly also egg transfer (see chapter 5 for more on these phenomena), some nests containing more than double the number of eggs found even in supernormal clutches (as it also true for "dump" nests in many Ducks and Geese).
"Biological Exuberance: Animal Homosexuality and Natural Diversity" - Bruce Bagemihl
